1. Field of the Invention
The present invention relates to a new use of enzymatic hydrolyzates of milk proteins. More particularly, the present invention relates to an agent for tyrosinase inhibition containing enzymatic hydrolyzates of milk proteins as an effective material for tyrosinase inhibition.
2. Discussion of the Background
Tyrosinase is known as an enzyme which may act as a catalyst for oxidization of tyrosin, other monohydric phenols or corresponding dihydric orthophenols with molecular oxygen and which widely occurs in plants such as mushrooms, potatoes, apples as well as in animal tissues. It is also known that tyrosinase is related to darkening phenomena at an injured portion of plant tissue, and is also related to formation of melanin pigment in various tissues of animals, especially in epidermal cells (Editorial Committee of Encyclopedia Chimica, Encyclopedia Chimica, Vol. 5, page 976, Kyohritsu Shuppan; 1960).
It is also known that pigmentation of melanin in epidermal cells or mucous membranes in Addison's disease is resulting from decrease in secretion of adrenal cortex hormones which antagonize melanotropin which in turn promotes tyrosinase activity (Editorial Committee of Encyclopedia Chimica, Encyclopedia Chimica, Vol. 1, page 65, Kyohritsu Shuppan; 1960).
Furthermore, it is said that tyrosinase is also related to degradation in freshness of foods.
Therefore, it has been strongly desired, in the industrial fields of pharmaceuticals, cosmetics, food and the like, to develop agents for tyrosinase inhibition and for prevention and therapy of symptoms resulting from undesirable effects of the activity of tyrosinase. Especially in the fields of cosmetic industry, earnest research has been actively made on cosmetics or medicines for external use for effective inhibition of tyrosinase, and many products containing agents for tyrosinase inhibition have been successively developed. There are known many agents for tyrosinase inhibition, for example, cystein, glutathione and vitamin C (Yutaka Mishima et al., Fundamental Dermatology, page 258, Asakura Shoten; 1973), Kojic acid (Nikkei Sangyo News Paper, May 24, 1988), arbutin (Kenichi Tomita, Preliminary Text for 20th F. J. Seminar, page 21, Fragrance Journal Company, Mar. 14, 1990), products of microorganisms belonging to the genus of Trichoderma (Unexamined Japanese Patent Application Gazette No. 2(1990)-145189).
In Examined Japanese Patent Application Gazette No. 58(1983) -17763, utilization of alkaline hydrolyzates of silk proteins in cosmetics as an agent for tyrosinase inhibition.
Conventional agents for tyrosinase inhibition, however, had more or less defects that they are unstable in the products, they have excessively potent function to melanocytes which produce melanin pigment, and they are too expensive due to the difficulty to obtain their raw materials, and they were not usable as cosmetics or medicines for external use from the view points of safety, preservability, reliability, economics and so on.
On the other hand, milk proteins and hydrolyzates thereof have been utilized in cosmetic products for various purposes such as moisturizing, film-forming (Unexamined Japanese Patent Application Gazette No 60(1985)-258102, Unexamined Japanese Patent Application Gazette No. 62(1987)-185100, Unexamined Japanese Patent Application Gazette No. 1(1989)-269499), and in the products of pharmaceutical and food industries for the purposes of increase in digestibility and absorbability, improvement in nutritional efficiency, and prevention from or treatment of allergy.
Recently, it has been reported that peptides included in milk protein hydrolyzates have physiological properties, for example, calcium absorption promoting property of .beta.-casein phosphopeptide and proliferation promoting property of Bifidobacteria of .kappa.-casein glycomacropeptide (Shokuhin Kogyo, Vol. 33, No. 1, page 31, 1990).
therefore, research has been actively made for the application of milk protein hydrolyzates in functional foods and drugs, however, it has not been known that peptides included in milk protein hydrolyzates have the activity of tyrosinase inhibition.
The inventors of the present invention have performed a research with respect to the agent for tyrosinase inhibition which has no defects in conventional agents for tyrosinase inhibition and which is usable for foods and drugs and which is stable and safe when it is used in such products, and found that enzymatic hydrolyzates of milk proteins surprisingly have activity of tyrosinase inhibition. The present invention is based on this discovery.
It should be noted that some of the inventors of the present invention and others have made inventions with respect to an agent for tyrosinase inhibition consisting of or containing lactoferrin or its hydrolyzates, and applications for patent have been filed in Japan by the same assignee of the present invention (Japanese Patent Application Nos. 2(1990)-169636 and 2(1990)-169637). Therefore, the objective substances of the present invention are the hydrolyzates of milk protein exclusive of lactoferrin, but when the present invention is actually carried out, it is not necessary to exclude lactoferrin from the milk protein as the raw material.